Well bores are commonly drilled into subterranean formations at an orientation which deviates from true vertical to increase hydrocarbon production from a given well and/or to reduce the unit cost of hydrocarbon recovery from a given well. For example, a deviated well bore penetrating a fractured formation can increase the drainage area defined by the well bore to substantially increase hydrocarbon production from the resulting well. The use of deviated well bores also increases the number of well bores which can be drilled and completed from a single offshore drilling platform having a set number of drilling slots. The ability to recoup the substantial fixed cost of constructing the offshore drilling platform is often enhanced as a function of the number of well bores which can be drilled and completed from the platform. A plurality of deviated or offset well bores can be drilled from any one drilling slot on an offshore drilling platform using current technology as evidenced, for example, by U.S. Pat. No. 5,330,007. A downhole template is employed to guide the drill string in a desired direction which is offset from the surface casing for the purpose of drilling an offset well bore.
The present invention recognizes a need for a downhole template which can be positioned and cemented in a main well bore to enable drilling and completion of an additional offset well bore from the main well bore using the template. One of the problems encountered in developing such a template is to define template configurations and procedures which more easily and cost-effectively enable circulating fluids past the template in the main well bore to cement the template therein and which also relatively easily and cost-effectively enable drilling and completion of an offset well bore using the resulting cemented template. Accordingly, it is an object of the present invention to provide a downhole template or system of downhole templates which is configured for circulating fluids past the templates when placed in a well bore. It is another object of the present invention to provide a process for circulating fluids past the template or system of templates in a main well bore, particularly for the purpose of cementing the templates in the main well bore. It is yet another object of the present invention to provide a template or system of templates which is reconfigured for drilling and completing one or more offset well bores from the main well bore. It is still another object of the present invention to provide a process for reconfiguring the template or system of templates from a fluid circulation configuration to drilling or completion configurations. It is a further object of the present invention to provide processes for drilling and completing one or more offset well bores from the main well bore using the template or system of templates. These objects and others are achieved in accordance with the invention described hereafter.